Implementation of microfluidic components in a microfluidic system

ABSTRACT

A system and method for integrating microfluidic components in a microfluidic system enables the microfluidic system to perform a selected microfluidic function. A capping module includes a microfluidic element for performing a microfluidic function. The capping module is stacked on a microfluidic substrate having microfluidic plumbing to incorporate the microfluidic function into the system.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/329,018 filed Dec. 23, 2002, which claims priority to U.S.Provisional Patent Application Ser. No. 60/409,489 filed Sep. 9, 2002,and U.S. Provisional Patent Application Ser. No. 60/410,685, filed Sep.13, 2002, the contents of which are herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a microfluidic system for handlingfluid samples on a microfluidic level. More particularly, the presentinvention relates to a system and method for implementing microfluidicfunctions in a microfluidic system.

BACKGROUND OF THE INVENTION

Microfluidic devices and systems provide improved methods of performingchemical, biochemical and biological analysis and synthesis.Microfluidic devices and systems allow for the performance ofmulti-step, multi-species chemical operations in chip-based microchemical analysis systems. Chip-based microfluidic systems generallycomprise conventional ‘microfluidic’ elements, particularly capable ofhandling and analyzing chemical and biological specimens. Typically, theterm microfluidic in the art refers to systems or devices having anetwork of processing nodes, chambers and reservoirs connected bychannels, in which the channels have typical cross-sectional dimensionsin the range between about 1.0 μm and about 500 μm. In the art, channelshaving these cross-sectional dimensions are referred to as‘microchannels’.

In the chemical, biomedical, bioscience and pharmaceutical industries,it has become increasingly desirable to perform large numbers ofchemical operations, such as reactions, separations and subsequentdetection steps, in a highly parallel fashion. The high throughputsynthesis, screening and analysis of (bio)chemical compounds, enablesthe economic discovery of new drugs and drug candidates, and theimplementation of sophisticated medical diagnostic equipment. Of keyimportance for the improvement of the chemical operations required inthese applications are an increased speed, enhanced reproducibility,decreased consumption of expensive samples and reagents, and thereduction of waste materials.

In the fields of biotechnology, and especially cytology and drugscreening, there is a need for high throughput filtration of particles.Examples of particles that require filtration are various types ofcells, such as blood platelets, white blood cells, tumorous cells,embryonic cells and the like. These particles are especially of interestin the field of cytology. Other particles are (macro) molecular speciessuch as proteins, enzymes and poly-nucleotides. This family of particlesis of particular interest in the field of drug screening during thedevelopment of new drugs.

SUMMARY OF THE INVENTION

The present invention provides a system and method for integratingmicrofluidic components in a microfluidic system to enable themicrofluidic system to perform a selected microfluidic function. Thepresent invention utilizes a capping module including a microfluidicelement for performing a microfluidic function. The capping module isstacked on a microfluidic substrate having microfluidic plumbing toincorporate the microfluidic function into the system.

According to one aspect, the invention provides a microfiltration systemin a microfluidic chip for separating a substance, such as a compound,moving through a closed channel system of capillary size into differentcomponents. The filtration system of the invention provides a filtrationmodule that can be assembled at low cost while providing an accuratemeans of filtering a large amount of compounds per unit of time. Themicrofiltration system integrates conventional membrane filtertechnology into a microfluidic system formed of glass, plastic or othersuitable material. The microfabricated filtration system may comprise asub-system designed to be inserted into a standard microfluidic systemto provide on-chip filtration. An illustrative filtration systemincludes two flow paths separated by a membrane, which separates asubstance flowing through a first flow path by size discrimination.Reservoirs are formed on either side of the membrane in communicationwith the flow paths. A microfabricated cap is affixed to the membrane todefine the reservoir on the top side of the membrane.

According to another aspect, an electromagnetic valve may beincorporated into a microfluidic system using a capping structure havingelectromagnetic valve components formed therein. The electromagneticvalve components include a membrane for selectively blocking flowthrough one or more communication ports in a substrate and an actuatorassembly for controlling the position of the membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a microfluidic system including a capping structurefor integrating a microfluidic function into the microfluidic system.

FIG. 2 illustrates a diagnostic microfluidic chip suitable for includinga microfiltration system according to an illustrative embodiment of theinvention.

FIG. 3 is a perspective, cross-sectional view of the microfiltrationsystem in the chip of FIG. 2 according to an illustrative embodiment ofthe invention.

FIG. 4 is a detailed view of the membrane on the microfiltration systemof FIG. 3.

FIG. 5 illustrates the microfabricated cap of the microfiltration systemof FIG. 3.

FIG. 6 is a top view of the microfiltration system of FIG. 3.

FIG. 7 is a top view of the diagnostic chip of FIG. 2 before assembly ofthe microfiltration system.

FIG. 8 is a top view of the diagnostic chip of FIG. 2 after assembly ofthe microfiltration system.

FIG. 9 a is a top view of a two port direct microfiltration systemaccording to an alternate embodiment of the invention.

FIG. 9 b is a perspective cross-sectional view of the microfiltrationsystem of FIG. 9 a.

FIG. 10 a is a top view of a three port direct microfiltration systemaccording to an alternate embodiment of the invention.

FIG. 10 b is a perspective cross-sectional view of the microfiltrationsystem of FIG. 10 a, with the microfabricated cap removed.

FIG. 11 illustrates an electromagnetic valve incorporated into amicrofluidic system according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a microfabricated filtration system forallowing on-chip filtration, purification or separation of a sample. Themicrofabricated filtration system may be used in a wide variety ofapplications, including, but not limited to blood separation andfiltration, microdialysis, microchemical analysis and synthesisapplications that require a filtration or dialysis subsystem and othermicrofluidic application. The present invention will be described belowrelative to an illustrative embodiment. Those skilled in the art willappreciate that the present invention may be implemented in a number ofdifferent applications and embodiments and is not specifically limitedin its application to the particular embodiments depicted herein.

As used herein, the term “microfluidic” refers to a system or device forhandling, processing, ejecting and/or analyzing a fluid sample includingat least one channel having microscale dimensions.

The terms “channel” and “flow channel” as used herein refers to apathway formed in or through a medium that allows for movement offluids, such as liquids and gases. The channel in the microfluidicsystem preferably have cross-sectional dimensions in the range betweenabout 1.0 μm and about 500 μm, preferably between about 25 μm and about250 μm and most preferably between about 50 μm and about 150 μm. One ofordinary skill in the art will be able to determine an appropriatevolume and length of the flow channel. The ranges are intended toinclude the above-recited values as upper or lower limits. The flowchannel can have any selected shape or arrangement, examples of whichinclude a linear or non-linear configuration and a U-shapedconfiguration.

The term “microfluidic element” as used herein refers to a component ina microfluidic system for performing a microfluidic function, including,but not limited to: passive check valves, active valves, pressuresensors, connecting channels, membrane filtration units, threaded tapsfor external connecting tubes, compression chambers, pumps, and othersthat may be known to those of ordinary skill in the art.

The term “membrane” or “filter” as used herein refers to a material ofany suitable composition and size which may used to separate or filtersubstances by size exclusion or other measures.

The term “substrate” as used herein refers to a support structure havingchannels formed therein for conveying a fluid.

The terms “cap” or “capping module” as used herein refer to a structure,which is the same size as or smaller than a substrate, having anyselected size or shape and formed of any selected material, and having amicrofluidic element. The capping module is configured to stack on orcommunicate with the substrate to fully or partially complete a fluidpath.

The term “substance” as used herein refers to any material used in amicrofluidic process, including, but not limited to chemical compounds,molecules, viruses, cells, particles, beads, buffers, or any othermaterial used in a microfluidic process.

The term “microfluidic function” as used herein refers to any operation,function or process performed or expressed on a fluid or sample in amicrofluidic system, including, but not limited to: filtration,dialysis, pumping, fluid flow regulation, controlling fluid flow and thelike.

The term “port” refers to a structure for providing fluid communicationbetween two elements.

As used herein, “pump” refers to a device suitable for intaking anddischarging fluids and can have different sizes, including microscaledimensions, herein referred to as “micropump.”

The present invention allows implementation of different microfluidicfunctions into a microfluidic chip using a capping module having amicrofluidic element for performing a microfluidic function. As shown inFIG. 1, a microfluidic chip 10 suitable for implementing an embodimentof the invention comprises a substrate 11 having one or more flowchannels 3, illustrated as a microchannel, disposed therein. The flowchannels transport fluid through the microfluidic system 10 forprocessing, handling, and/or performing any suitable operation on aliquid sample. The microfluidic system 10 may comprise any suitablenumber of flow channels 3 for transporting fluids through themicrofluidic system 10.

As shown in FIG. 1, the flow channel 3 is formed in a substrate 11, andmay connect to the surface of the substrate via one or morecommunication ports 13 a and 13 b. A capping module 15 including amicrofluidic element 18, such as a filter, one or more valves, pressuresensors or other component for performing a microfluidic function, isplaced over the substrate 11 to form a closed fluid path. According toan alternate embodiment, the capping module may include a connectorchannel for re-routing fluid flow through the microchannel aroundanother structure. The illustrative substrate 11 includes twocommunication ports 13 a, 13 b, each connecting unconnected segments 3a, 3 b of the flow channel 3 to the substrate surface, though oneskilled in the art will recognize that variations may be made in thesize, number and configuration of the communication ports and flowchannels.

The illustrative capping module 15 may include connector ports forinterfacing with the communication ports of the substrate, and/or achamber 12 or channel to provide a fluidic path between the firstconnector port and the second connector port. One skilled in the artwill recognize that the capping module may have alternate configurationsand is not limited to the embodiment shown in FIG. 1.

Using the capping module 15, microfluidic functions, such as filtration,dialysis, pumping, flow control and so on, may be integrated into themicrofluidic system 10 without requiring significant modification of thesubstrate 11. A substrate including any number and arrangement ofconduits or channels 3 for conveying fluids can be transformed into afunctional fluidic circuit by selecting and placing one or more cappingmodules 15 with a functional microfluidic element 18 on the substrate,i.e. chip. According to an illustrative embodiment, the same automated“pick and place” surface mount equipment technology used to makeintegrated circuits may be used to form fluidic circuits on a substratehaving microchannels using various capping structures. Suitable pick andplace equipment is manufactured by Manncorp, Inc. (Huntingdon Valley,Pa.), among others.

To fabricate a fluidic circuit, the channels 3 in the substrate 11 maybe manufactured by chip microfabrication. The channels or plumbing maybe fabricated by etching half-channels in a first substrate, followed bybonding and/or lamination of a second substrate to enclose thehalf-channels, forming a microchannel. The substrate may be formed ofone or more layers containing etched channels if more complex fluidicnetworks are required. The communication ports may then be fabricated inthe substrate to connect the microchannel to an exterior surface of thesubstrate. Suitable techniques for fabricating the communication portsinclude drilling, laser etching, powder blasting or other techniquesknown in the art. After the fabrication of the substrate andcommunication ports, a capping module having a desired functionality isbonded to the substrate to form a microfluidic component in the largermicrofluidic circuit.

A variety of capping module number and sizes may be bonded to thesubstrate to impart various microfluidic functions to form amicrofluidic system. The capping modules may be removable andreplaceable so that a substrate may be re-used.

According to the illustrative embodiment, the capping module has across-sectional dimension of between about 1 millimeter and about 5centimeters, though those skilled in the art will recognize that theinvention is not limited to this range. The capping module may be formedof any suitable material, including, but not limited to plastic, glass,silicon and other materials known in the art.

FIG. 2 illustrates the architecture of an illustrative microfluidicdiagnostic chip that may be fabricated according to the teachings of theinvention. The diagnostic chip 20 may include one or more microfluidiccomponents, alone or in combination, configured to facilitate processingof a sample. For example, as shown, the diagnostic chip 20 includes amicrofiltration system 100 for separating substances in solution, suchas separating selected particles from cells or other particles in asuspension. The diagnostic chip 20 may further include one or morereservoirs 90 for storing and supplying sample, reagent or othercompounds to the system, as well as one or more waste reservoirs 91 forcollecting sample waste. The diagnostic chip may further include one ormore aliquoting, mixing and incubation components, such as an on-chipsample dilution system, for processing a sample, such as performing amixture of a specific amount of sample and reagent. For example, theillustrative system includes a mixing component 60 and an incubationregion 61. The chip may also include a detector 70 for analyzing afiltered product from the microfiltration system 100. The detector 70may utilize any suitable detection modality, including, but not limitedto fluorescence, electrochemical analysis, dielectrophoresis, andsurface plasma resonance (SPR), radio-frequency, thermal analysis andcombinations thereof. The chip 10 may employ valves for selectivelycontrolling the flow of fluid through the channels and one or more driveunits, located on or off the chip, for driving the movement of fluidthrough the channels 3 of the chip. One skilled in the art willrecognize that the microfluidic system is not limited to the diagnosticchip of FIG. 2 and that variations in the configuration, position,number and combination of the various microfluidic components may bemade in accordance with the present invention.

The filtration system 100 of the present invention integratesconventional membrane filter technology into a microfluidic chip using acapping module. The filtration system can be inserted into an existingmicrofluidic chip to enable filtration of particles, cells or othersubstances in suspension without requiring significant or expensivemodification of the chip structure.

FIGS. 3, 4 and 6 illustrate a microfabricated filtration subsystem 100suitable for implementation in the microfluidic system of FIG. 2according to one embodiment of the invention. FIG. 5 illustrates thecapping module 15 used to fabricate the filtration system 100 accordingto one embodiment of the invention. The filtration subsystem is utilizedto separate a substance, such as a sample comprising a mixture ofparticles and fluid, through a membrane 110 and subsequently collect theseparated components. According to an illustrative embodiment, thefiltration subsystem is used to separate blood cells from plasma, thoughone skilled in the art will recognize that other applications areincluded in the invention. According to other applications, thefiltration system may be used to separate viruses from cells, beads fromcells, chemical compounds, molecules or other substances that a membranemay be used to separate. As shown the filtration subsystem 100 is formeddirectly on the microfluidic chip to add filtration capability to thechip without requiring significant modification or expense.

The filtration subsystem 100 utilizes a conventional membrane filter 110separating two flow paths in the substrate 11 to provide small volumecontrollable filtration of a sample. The illustrative filtration systemis a four-port transverse filter, which includes a first fluid flow path120 for supplying a substance to the filtration system, such as amixture of particles and fluid, and a second fluid flow path 130 forreceiving and conveying a filtered product (i.e., a filtrate) from thefiltration system. The first fluid flow path 120 includes a firstcommunication port, illustrated as a first inlet channel 121 thatintersects the filtration system at a first inlet 121 a. The first fluidflow path 120 includes a second communication port, illustrated as afirst outlet channel 122 including an outlet 122 a from the filtrationchamber for receiving and conveying a retentate of the substance fromthe filtration system. The second fluid flow path includes an inletchannel 131 intersecting a filtrate chamber below the membrane 110 at asecond inlet and a second outlet channel 132 for transferring thefiltered product from the filtration system. The second fluid flow path130 may include a carrier fluid for conveying the filtered product. Aflow source drives the flow of the mixture through the filtration systemto effect separation of the components through the membrane. The flowsource may comprise an off-chip syringe pump, a microfabricatedperistaltic pump, a microfabricated syringe, or any suitable flow sourceknown in the art, such as those described in U.S. Provisional PatentApplication Ser. No. 60/391,868 entitled “Microfluidic System andComponents”, (Attorney Docket Number CVZ-019-2), the contents of whichare herein incorporated by reference.

The illustrative microfabricated filtration system 100 has a relativelysmall footprint (less than about one mm²), resulting in a compactstructure, low cost and relatively simple fabrication. The particleseparator further provides relatively low strain rates with reduced orno blockage. The amount of fluid retained can be significant, ifdesired, and the design is scalable and repeatable for additionalparsing steps, if desired.

The filtration subsystem of the present invention may be formed byproviding a microfluidic chip including an intersection 101 of the twoflow channels 120, 130. The assembly process integrates simple batchfabricated components, and is relatively simple and low cost at highvolume. According to an illustrative embodiment, the chip forms a recess140 in communication with the second flow channel 130 at theintersection 101. The first flow channel 120 is initially separated fromand divided by the recess 140. A suitable membrane 110 is affixed to themicrofluidic chip, using an appropriate adhesive or other suitablefastening mechanism, to cover the recess, thereby defining a reservoirbelow the membrane for receiving the filtered product and transmittingthe filter product through the second flow channel 130. The membrane maycomprise any suitable filtering membrane known in the art.

The illustrative microfabricated capping module 15, shown in FIG. 4, isaffixed above the membrane 110 to define a filtration chamber 161 incommunication with the first flow channel 120. The cap 15 may be affixedusing an appropriate adhesive or other suitable fastening mechanism. Theillustrative capping module 15 includes an inlet 162 and an outlet 163in communication with the filtration chamber to connect the first flowchannel 120 with the filtration chamber 161 and enable flow of acomposition to be filtered through the filtration chamber over themembrane. Alternatively, the membrane 110 is affixed directly to thecapping module 15 and the capping module is affixed to the substrate tointegrate the filtration system onto the substrate. One skilled in theart will recognize that the capping module is not limited to theillustrative embodiment and that variations may be made in accordancewith the teachings of the invention.

FIG. 7 illustrates the microfluidic system 10 including channels 3 priorformed therein prior to assembly of the capping module 15 including themembrane 110. FIG. 8 is a top view of the capped microfluidic system 10incorporating filtering capability.

The composition to be filtered is introduced to the filtration subsystemfrom the inlet channel and passes into the filtration chamber and overthe membrane 110. The components of the substance are fractionated bythe membrane 110, with the smaller components, such as plasma, passingthrough the membrane, into the reservoir 140 and through the second flowchannel 130. The remaining portion, such as blood cells, passes throughthe filtration chamber to the outlet of the first flow channel 120.

According to the illustrative embodiment, the substrate of themicrofluidic chip may be formed of glass, plastic, silicon, quartz,ceramics or any other suitable material. In a microfluidic chipmanufactured from glass, the chip may comprise two layers: the chip andthe cap affixed to the chip to define the filtration subsystem. In amicrofluidic chip formed of plastic, the components may be stamped intothe plastic substrate.

According to an alternate embodiment, shown in FIGS. 9 a and 9 b, themicrofiltration subsystem may comprise a two-port direct filter 180comprising a membrane 110 inserted into a fluid flow path 181. As shown,the two-port direct filter 181 comprises a fluid flow path 181 formed ina microfluidic substrate, which is divided into two sections 181 a, 181b. The second section 181 b defines a recess 182 and the membrane 110 isadhered over the recess to define a filtrate chamber for receiving afiltered product. A microfabricated cap 15 including a recess 186defining a filtration chamber is attached to substrate above themembrane to connect the flow path 181. The substance to be filtered isconveyed through the fluid flow path 181 into the filtration chamber 186and passes through the membrane 110. The membrane 110 separates thesubstance by trapping larger molecules and the filtered product,comprising the remaining molecules, passes through the membrane alongthe fluid flow path 181 into the recess 182 and out of themicrofiltration system for further analysis, processing collection, etc.

According to yet another embodiment, shown in FIGS. 10 a and 10 b, themicrofiltration system may comprise a three port direct filter 190. Thethree port direct filter 190 includes two inlet flow channels 191, 192for inputting two samples to a filtration chamber 195 and a singleoutlet channel 193 for conveying a filtered product from the filter 190.The three-port direct filter includes a microfabricated cap 15 definingthe filtration chamber and a membrane 110 separating the filtrationchamber from the outlet channel 193. In operation, two samples may beprovided through the inlet channels 191, 192. The samples mix togetherin the filtration chamber 195 and the sample mixture is filtered throughthe membrane, which separates the components of the sample mixture. Thefiltered product that passes through the membrane is conveyed throughthe outlet channel for further processing, analysis, collection etc.

One skilled in the art of membrane based separations will recognize thatthe filtration system described here can be used to implement on-chipseparations of all types for which membranes may be found, includingseparating molecules by size or beads from molecules or small particlesfrom large particles or viruses from cells or other separations known tothose skilled in the art.

According to another embodiment of the invention, the capping module 15may be used to incorporate an electromagnetic valve into a microfluidicsystem. An example of an electromagnetic valve component housed in acapping structure for implementation in a microfluidic system accordingto the teachings of the invention is shown in FIG. 11. As shown, theelectromagnetic module 150 comprises a cap 15 defining an interiorchamber 151, a membrane 154 for selectively blocking flow through one orboth of the communication ports in the substrate and an actuatorassembly 160 for deflecting the membrane 154. According to theillustrative embodiment, the actuator assembly comprises a coil 162 anda magnet 164. One skilled in the art will recognize that other suitablemeans for deflecting the membrane may be used, including piezoelectricactuators.

The electromagnetic capping module 110 may be stacked on the substrate11 such that the membrane, when deflected, blocks one or more of thecommunication ports 13 a and 13 b. The electromagnetic capping module110 thus integrates a valve for selectively blocking flow through thechannel 3 into the microfluidic flow path. As described above, theelectromagnetic capping module may be placed on the substrate usingautomated “pick and place” equipment or through any suitable means knownin the art.

One skilled in the art will recognize that the capping module is notlimited to the illustrative embodiment and that other elements may beimplemented to add other microfluidic functions, in addition to or inplace of, filtration and flow control.

The microfiltration system of the present invention advantageouslycombines the power and scope of conventional membrane technology withthe small volume dynamic flow control inherent inmicrofabricated/microstructure microfluidic systems. The presentinvention provides cost effective mixing of any suitable polymermembrane with a microfluidic network. The microfiltration system issimple and inexpensive to add to a microfluidic system, as theincremental cost of assembling the microfiltration system in amicrofluidic chip is relatively low above the cost of the microfluidicsystem itself A microfluidic system according to the present inventionmay comprise one or more of the above-described components, alone or incombination with other components.

The present invention has been described relative to an illustrativeembodiment. Since certain changes may be made in the above constructionswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are to cover allgeneric and specific features of the invention described herein, and allstatements of the scope of the invention which, as a matter of language,might be said to fall therebetween.

1. A microfluidic system, comprising: a first microchannel formed in asubstrate; a first communication port coupling the first microchannel toa surface of the substrate; and a capping module having a microfluidicelement for performing a microfluidic function, wherein the cappingmodule is adapted to be stacked on the substrate and placed incommunication with the microchannel to introduce the microfluidicfunction into the microfluidic system.
 2. The system of claim 1, furthercomprising a second communication port connecting a second microchannelto a surface of the substrate.
 3. The system of claim 2, wherein thecapping module includes a chamber for coupling the first microchannel tothe second microchannel.
 4. The system of claim 1, wherein themicrofluidic element comprises a membrane.
 5. The system of claim 1,wherein the microfluidic element comprises one of a valve for regulatingfluid flow through the microchannel, a pressure sensor and amicrofluidic pump.
 6. The system of claim 1, wherein the capping moduleis bonded to the substrate to integrate the microfluidic function intothe microfluidic system.
 7. The system of claim 1, wherein the cappingmodule has a cross-sectional dimension of between about 1 millimeter andabout 5 centimeters.
 8. The system of claim 2, wherein the cappingmodule further includes a membrane for selectively blocking saidcommunication port, and an actuator assembly for controlling a positionof the membrane.
 9. The system of claim 1, wherein the capping modulehas a recess and a membrane covering the recess to form a chamber,wherein the cap is adapted to be assembled on the substrate such thatthe membrane covers the first communication port.
 10. The system ofclaim 1, wherein the capping module includes: a membrane for separatinga substance into a first and second component; a first flow path fortransmitting a substance; a first reservoir disposed above the membraneand in communication with the first flow path for receiving thesubstance.
 11. The system of claim 10, wherein the substrate forms asecond flow path for receiving the second component of the substance andthe substrate forms a second reservoir below the membrane for receivingthe first component of the substance when the capping module is stackedthereon.
 12. The system of claim 11, further comprising a first flowsource in communication with the first fluid path for inducing a flow inthe substance.
 13. The system of claim 1, wherein the substrate has aplurality of microchannels formed therein, wherein each microchannelincludes one or more communication ports for connecting the microchannelto a surface of the substrate.
 14. The system of claim 13, furthercomprising a plurality of microfluidic capping modules, each havingassociated therewith a microfluidic element for performing amicrofluidic function, one or more of said microfluidic capping modulesfor placement on the substrate in fluid communication with one or moreof the microchannels to incorporate the associated microfluidic functioninto the system.
 15. A capping module for a microfluidic system,comprising: a substrate; and a microfluidic element disposed on thesubstrate for performing a microfluidic function, wherein the cappingmodule is adapted to be stacked on a microfluidic system having amicrochannel formed therein so that the microfluidic element is disposedin communication with the microchannel to introduce the microfluidicfunction into the microfluidic system.
 16. The capping module of claim15, further comprising a chamber formed in the substrate, wherein thechamber is placed in fluid communication with the microchannel when thecapping module is stacked on the microfluidic system.
 17. The system ofclaim 15, wherein the microfluidic element comprises a membrane.
 18. Thesystem of claim 15, wherein the microfluidic element comprises a valve.19. The system of claim 15, wherein the microfluidic element comprises apressure sensor.
 20. The system of claim 15, wherein the microfluidicelement comprises a microfluidic pump.